观测指示器 meaning in Chinese

sight indicator
viewing indicator

Specification for sight - flow indicators for tank overflow systems
储槽溢流装置用流量观测指示器规范
Specification for indicators , sight , liquid level , direct indirect reading , tubular glass plastic
直接和间接读取液位的管形玻璃和塑料观测指示器规范
Standard specification for indicators , sight , liquid level , direct and indirect reading , tubular glass plastic
直接和间接读取液位的管形玻璃和塑料观测指示器标准规范